B1.2 Proteins
Understandings:
Form and function
Molecules
B1
HL
Key words:
R group
Primary
Secondary
Tertiary
Quaternary
Alpha helix
Beta pleated sheet
Ionic bonds
Hydrogen bonds
Disulfide bonds
Hydrophobic interactions
Hydrophilic interactions
Conjugated
Prosthetic group
Globular
Fibrous
Insulin
Collagen
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B1.2.6—Chemical diversity in the R-groups of amino acids as a basis for the immense diversity in protein form and function
The backbone of an amino acid is always the same.
The R group changes.
The properties of the R group give the amino acid different properties.
All amino acids have Carbon, Hydrogen, Oxygen and Nitrogen
Cysteine and Methionine also contain Sulfur
Protein structure
The way the amino acids (particularly the R groups) interact together dictates the three dimensional structure of proteins.
B1.2.7—Impact of primary structure on the conformation of proteins
Primary structure
The primary structure is simply the order of amino acids strung together like beads on a string
B1.2.8—Pleating and coiling of secondary structure of proteins
Secondary structure
Secondary structure is the interactions of one part of the polypeptide backbone with another part of the backbone.
The R groups are not involved the secondary structure
What is a hydrogen bond?
Hydrogen bonds form between the oxygen on the carboxyl end of one amino acid with the hydrogen on the amino end of another amino acid (in the same polypeptide)
Alpha helix
Beta pleated sheet
B1.2.9—Dependence of tertiary structure on hydrogen bonds, ionic bonds, disulfide covalent bonds and hydrophobic interactions
Tertiary structure
Ionic bonds
Hydrogen bonds
Disulfide bonds
Hydrophobic/philic interactions
Ionic bond
Parts of amino acids can become charged by gaining or losing hydrogen ions.
Disulfide bond
Disulfide bonds are always formed between two cysteine amino acids
Because it is a covalent bond it is the strongest of all the interactions
B1.2.10—Effect of polar and non-polar amino acids on tertiary structure of proteins
Polar amino acids are hydrophilic
Non-polar amino acids are hydrophobic
This quality allows the protein to fold in a certain way when in solution
The polarity of amino acids also allow them to embed in the cell membrane
Most transmembrane proteins are embedded in the membrane using α-helices composed of nonpolar amino acids.
B1.2.11—Quaternary structure of non-conjugated and conjugated proteins
Quaternary structure
The same interactions that affect the tertiary structure can also join more than one separate polypeptide chain together
Non conjugated - More than one polypeptide chain joined together
Conjugated - May also contain a non amino acid molecule - this would be called a prosthetic group
Describe the protein structure of insulin
Collagen is a very important structural protein.
It consists of three polypeptides braided together like a rope
Describe the quaternary structure of haemoglobin
Nature of Science
Technology allows imaging of structures that would be impossible to observe with the unaided senses. For example, cryogenic electron microscopy has allowed imaging of single-protein molecules and their interactions with other molecules.
B1.2.12—Relationship of form and function in globular and fibrous proteins
Copy and correct the following table
Fibrous proteins | Globular proteins |
E.g. insulin, haemoglobin | Fewer examples |
Soluble | Elongated, strand like |
Very little tertiary structure | Metabolic functions |
Spherical | Many examples |
Relatively less mass in body | Structural functions |
E.g. collagen, keratin | Insoluble |
Tertiary structure important | Relatively more mass in body |
Copy and correct the following table
Fibrous proteins | Globular proteins |
Elongated, strand like | Spherical |
Insoluble | Soluble |
Structural functions | Metabolic functions |
Fewer examples | Many examples |
Relatively more mass in body | Relatively less mass in body |
E.g. collagen, keratin | E.g. insulin, haemoglobin |
Very little tertiary structure | Tertiary structure important |
Insulin
Insulin is a peptide hormone
It binds to receptors on the surface of cells
It has a unique pattern on its surface formed by the tertiary structure
Collagen
Collagen is an important structural protein
It forms long rope like fibres
It has high tensile strength
Primary component of skin, bone, tendons, ligaments
Can you…
Describe the structure of proteins?
Describe the benefits of cryogenic electron microscopy?
Contrast globular and fibrous proteins and give an example of each?